In many BIOS's, in addition to the basic boot sequence, there is usually an additional setting that allows you set boot priority among the devices attached. i.e. with two DVD drives attached, you should, in theory, have a setting that allows you to tell the PC which DVD drive to boot from. I have two SATA hard drives and no IDE hard drives, and I had to tell the PC not only in what order to boot (CD, HDD, etc), but also which device has boot priority. I have no idea if your BIOS has such a setting, but I do remember that in my BIOS those settings aren't necessarily grouped with the boot sequence settings and it's something you haven't mentioned doing.